"The game uses various video configurations ranging from the Hold and Modify (HAM6) display to Hires (16 colours) to Half-Brite.

The game view is in 64 colours Half-Brite, but this meant we needed to work extra on the game speed. Not only did we have to blit 50% more versus a 16 colour game, but we also had 50% less processor bandwidth time to do it.

60 fps was not compatible with our idea to put everything on-screen that we wanted, so a 30 fps goal was decided.

We started with sprites multiplexing, enabling 44 moving objects on screen in 16 colours. However, the limitation was that we decided to only draw enemies with them, and 44 aliens to shoot at were more than enough. Also, because we are in Half-Brite, each sprite uses a mask for its true shadow and for the hit colour.

Then we moved to make a blitter engine. It was decided that it would be used for all shooting. This meant not using the blitter interrupt because we had over 50 shots on-screen; it would not have been a wise idea otherwise.

We also decided that we would not use double buffer display, and we used bank mode for all Amiga 'custom chip' addressing. This limited us to a 64KB view area (320x200x6 screen takes under 48KB).

The all direction scroll is one of the most efficient memory and CPU wise, but uses processor block copy. First, because it enables the block data (two banks or 128K) to be placed in 'FAST' memory, and second because we support many operations on blocks that the blitter cannot do.

Then it supposes that the blitter engine has to take into account the copper-cut. Because the screen wraps and the addressing does not, an object blitted on the cut requires a double 'blit and restore' operation. Several shots can pre-calculate their speed and position enabling to pass over the cut.

Because of the very large background maps used in OVERDRIVE, we use a 'Virtual ROM' mechanism to get the map on disk and not eat precious memory. Machines with more than 1MB will be able to load further into the game without having to wait for a free buffer." [Source: Stephan Schaem, coder]

[2] OVERDRIVE was released separately as 512K and 1MB versions. The 512K release was only available as a direct purchase from publisher Infacto, and lacked advanced features including multiple floppy drive support, the ability to launch the game from WB, multitasking and a quit back to WB option.

[3] Game uses 'Pre-loading' and 'Virtual ROM', which offer greater performance for single floppy-based systems. 'Pre-loading' enables disk activity while playing. For example, when in the ship selector, level 1 will load and a 'Virtual ROM' disk will be created. 'Virtual ROM' is used to store the game background maps. If the disk is removed during play, the game will enter PAUSE mode as it will interpret this as if you just removed RAM from your Amiga. Also 'Virtual ROM' frees up precious memory, which can be used for extra gfx, sounds and more.

[4] Game requires a blank disk to be inserted for savegames and high score saves when users are prompted for the last disk.

[5] Reportedly, the original release of OVERDRIVE is buggy and prone to crashes (e.g. choosing an option too quickly on the main menu screen will cause a crash when the game is loading - avoid this by waiting 5 sec before making a choice; background scrolling is absent on level 4; game very occasionally freezes on loading starfield screen). The WHDLoad HD patch fixes these bugs, thus making it possible for players to complete the game (see HERE for further details).

[6] OVERDRIVE(demo) is available for download on AminetHERE (dir: /game/demo/Overdrive2.lha).

TRIVIA: OVERDRIVE was publisher Infacto's one and only Amiga game release.